Dopamine-depletion and increased alpha-synuclein load induce degeneration of cortical cholinergic fibers in mice

Cognitive dysfunction can be common among Parkinson's disease (PD) patients, and multiplication of the gene alpha-synuclein (alpha syn) increases the risk of dementia. Here, we studied the role of dopamine-depletion and increased asyn load and aggregation on cholinergic structures in vivo. Wild-type (WT) and mice with A30P asyn overexpression were treated subacutely with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MFTP), and the number of cholinergic cells in their nucleus basalis magnocellularis-substantia innominata (NBM-SI), their cortical fiber density and their expression of different genes 1 day or 90 days after the last MPTP-injection were measured. Long-term dopamine depletion decreased the expression of choline acetyl transferase (ChAT) in the NBM-SI of WT mice, but no neuron loss was observed. In contrast, cortical cholinergic fiber density was decreased three months after MPTP-injection. Increased brain-derived neurotrophic factor expression could maintain cholinergic functions under these conditions. Expression of A30P alpha syn in six-months-old transgenic mice resulted in decreased tyrosine receptor kinase B expression, and lower cortical cholinergic fiber density. Dopamine-depletion by MPTP induced cholinergic cell loss in the NBM-SI and increased cortical fiber loss. Our findings may explain why cholinergic cells are more vulnerable in PD, leading to an increased probability of dementia. (C) 2011 Elsevier B.V. All rights reserved.